1. Field of Invention
The present invention relates to photoresist materials which can be used as an ion etch barrier without additional processing steps.
2. Description of the Prior Art
The manufacture of integrated circuits requires an accurate and precise method to form patterns on wafers to delineate areas for subsequent doping, isolation, interconnections, and the like. Photolithography is generally used to pattern a semiconductor wafer. In conventional positive photolithographic patterning, a photoresist material is spun onto a semiconductor surface and then exposed through a patterned mask to an appropriate radiation, such as ultraviolet light, electron beam, X-ray or the like. The mask allows light or radiation to strike the photoresist only where the pattern is to be formed, thus exposing the resist corresponding to the pattern. The wafer is then developed for example, by subjecting the wafer to an organic-based wash to develop and remove the exposed resist.
Another commonly used photolithography technique makes use of a negative resist process. Negative resist processes allow the exposed photoresist compound to remain on the workpiece after developing. One such negative resist method is diffusion-enhanced silylating resist (DESIRE). The DESIRE process uses photoactive compound (PAC) which is mixed into the photoresist to form barriers to a reactive ion etch.
Photoresist materials are widely used in the semiconductor industry. The photoresist material is easily patterned by a mask and developed. The pattern created can then be created on an underlying substrate by etching. As a result, much effort has been made in using a reactive ion etch (RIE) barrier in combination with photoresists and in chemically or physically altering a photoresist after patterning so that it will have the qualities of an RIE barrier.
U.S. Pat. Nos. 5,094,936, 5,041,362, 5,286,607 and 5,356,758 are examples of multiple step processes used to render photoresist layers resistant to reactive ion etching. In these processes, a photoresist material is applied to a substrate, exposed to a light source, and then subjected to a conversion treatment with a silicon-liberating compound such as hexamethyldisilazane, usually in a gaseous state. These multiple step process result in increased processing difficulty time and expense.
Attempts have been made to provide a photoresist material that can be used as an ion etch barrier. For example, U.S. Pat. No. 5,262,273 describes a photoresist material that is the reaction product of a novolac resist and a substituted silane compound. Further, U.S. Pat. No. 4,665,006 describes a polyamine system having organopolysiloxane segments sensitized by an onium salt.
None of the photoresist composition or processes described previously are effective in the dry etching of deep via holes (remove from 50 microns to 100 microns of semiconductor materials such as InP and related materials) for backside grounding connection by means of ECR (Electron Cyclotron Resonance Radio Frequency Discharges) etching technology. The silylated photoresists described thus far are too thin and erode shortly after removal by a few microns of semiconductor material (InP) under ECR etching conditions. The photoresist materials will crack if they are intentionally coated too thickly.